1. Field of the Invention
This invention relates broadly to the field of crossbows. More particular, this invention relates to the use of at least one no let-off cam at the limb tip of a crossbow for increasing the energy stored in the bow limbs and for increasing the initial force applied to the shot.
A. State of the Art
Crossbows in use at the present time include traditional crossbows having flexible limbs which do not include cams at their limb tips and conventional compound crossbows having let off cams at their limb tips. Both the traditional crossbow and the conventional compound crossbow operate in the same general manner. A stirrup on the crossbow is placed against the ground and the shooter's foot is placed within the stirrup. The shooter then draws the bowstring cable against the force of the bow limbs storing energy in the bow limbs. When the bowstring cable is fully drawn, it is held in position by a crossbow trigger mechanism. A bolt is placed on a guide in the crossbow in proximity to the cocked bowstring cable. When the shooter actuates the trigger mechanism, the bowstring cable is released and the energy stored in the bow limbs propels the bolt from the crossbow.
In traditional crossbows, the bowstring cable is directly attached to the outer ends of the bow limbs, so that the amount of force exerted on the bowstring cable, and thus the amount of energy stored in the limbs, is substantially proportional to the distance that the bowstring cable is displaced from the initial, or brace, position. In conventional compound crossbows, the bowstring cable is attached to eccentric cams located on axles journalled in the outer ends of the bow limbs. As the bowstring cable is drawn, it rotates the eccentric cams against the countervailing force of an anchor cable which is also attached to the eccentric cams. The force exerted on the bowstring cable, and the amount of energy stored in the limbs, is dependent upon the force required to rotate the eccentric cams. In conventional compound crossbows, the eccentric cams provided let-off so that the amount of force exerted on the bowstring cable at full draw was less than the force exerted on the bowstring cable at peak weight. In such prior art compound crossbows, it was assumed that let off was necessary to enable the shooter to more accurately aim the crossbow.
The let off in such conventional compound crossbows was generally achieved by shaping the eccentric cams so that less draw force was required to rotate the cam after the crossbow had been drawn to its peak weight. For example, the distance between the axle on which the eccentric cam was mounted and the path on which the bowstring cable travels might be reduced after peak weight or the distance between the axle on which the eccentric cam was mounted and the eccentric path on which the anchor cable travels might be reduced after peak weight. A reduction of the force exerted on the bowstring cable after let-off caused the energy stored in the bow limbs to be reduced. In addition, because there was less energy stored in the bow limbs after let off, when the crossbow was shot, the bolt traveled with less velocity and with less kinetic energy than if it had been shot at peak weight.